This study seeks to unravel the growth and environmental contributions to refractive changes of the sub-human primate eye. One goal will be to make accurate evaluations of the amount of accommodation required and developed in monkeys as related to the optical components of the individual animal eye and to relate the amount of accommodation and component relationships to fixation distance, retinal image size and blur, pupil size, spasm of accommodation and intraocular pressure to the changes occurring in refractive state with growth and environmental conditions including near visual space. Since only 70-80 per cent of the animals in the near visual space develop myopia, the differences between those monkeys who do develop myopia and those that don't is of particular interest. A second approach will be to try to set up longitudinal studies in monkeys which permit testing variables such as diet, particularly high intake of sweets, and the effects of drugs such as eserine and atropine on the development of myopia. We are also interested in the changes which occur in hypermetropia and the possibility of reducing the amount of hypermetropia in monkeys through environmental manipulation. These studies should have implications for human refractive conditions. A third approach is a series of laboratory studies on monkey eyes using manometers and implanted radiosonde transducers which require no direct connections to determine the effects of accommodation, convergence and drugs on the pressure relationships in the anterior and vitreous chambers of the eye in order to determine their possible contribution to the development of myopia. Blood flow relationship in the eye under different conditions will also be determined with the aid of radioactive microspheres.